drm/radeon: update wait_for_vblank for evergreen+

Properly wait for the next vblank region.  The previous
code didn't always wait long enough depending on the timing.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/evergreen.c

@@ -316,6 +316,27 @@ void evergreen_fix_pci_max_read_req_size(struct radeon_device *rdev)
 	}
 }
 
+static bool dce4_is_in_vblank(struct radeon_device *rdev, int crtc)
+{
+	if (RREG32(EVERGREEN_CRTC_STATUS + crtc_offsets[crtc]) & EVERGREEN_CRTC_V_BLANK)
+		return true;
+	else
+		return false;
+}
+
+static bool dce4_is_counter_moving(struct radeon_device *rdev, int crtc)
+{
+	u32 pos1, pos2;
+
+	pos1 = RREG32(EVERGREEN_CRTC_STATUS_POSITION + crtc_offsets[crtc]);
+	pos2 = RREG32(EVERGREEN_CRTC_STATUS_POSITION + crtc_offsets[crtc]);
+
+	if (pos1 != pos2)
+		return true;
+	else
+		return false;
+}
+
 /**
  * dce4_wait_for_vblank - vblank wait asic callback.
  *
@@ -326,21 +347,28 @@ void evergreen_fix_pci_max_read_req_size(struct radeon_device *rdev)
  */
 void dce4_wait_for_vblank(struct radeon_device *rdev, int crtc)
 {
-	int i;
+	unsigned i = 0;
 
 	if (crtc >= rdev->num_crtc)
 		return;
 
-	if (RREG32(EVERGREEN_CRTC_CONTROL + crtc_offsets[crtc]) & EVERGREEN_CRTC_MASTER_EN) {
-		for (i = 0; i < rdev->usec_timeout; i++) {
-			if (!(RREG32(EVERGREEN_CRTC_STATUS + crtc_offsets[crtc]) & EVERGREEN_CRTC_V_BLANK))
+	if (!(RREG32(EVERGREEN_CRTC_CONTROL + crtc_offsets[crtc]) & EVERGREEN_CRTC_MASTER_EN))
+		return;
+
+	/* depending on when we hit vblank, we may be close to active; if so,
+	 * wait for another frame.
+	 */
+	while (dce4_is_in_vblank(rdev, crtc)) {
+		if (i++ % 100 == 0) {
+			if (!dce4_is_counter_moving(rdev, crtc))
 				break;
-			udelay(1);
 		}
-		for (i = 0; i < rdev->usec_timeout; i++) {
-			if (RREG32(EVERGREEN_CRTC_STATUS + crtc_offsets[crtc]) & EVERGREEN_CRTC_V_BLANK)
+	}
+
+	while (!dce4_is_in_vblank(rdev, crtc)) {
+		if (i++ % 100 == 0) {
+			if (!dce4_is_counter_moving(rdev, crtc))
 				break;
-			udelay(1);
 		}
 	}
 }